Dolphins belong to a marine order called Cetacea (pronounced se-tay-shi-a) which is the group name given to those mammals that are born and live the whole of their lives in the sea. By definition this includes the Whale, Dolphin, Porpoise, Grampus and the Manatee, but would exclude such animals as the Seal and Walrus who have come on to land to give birth.

Cetaceans can be divided into two main orders: The Mysticeti and the Odontoceti.